1. Field of the Invention
This invention relates generally to a communications system and, more particularly, to a method for interference management of a processing communications satellite to reduce intra-system interference in a satellite based cellular communications system.
2. Discussion of the Related Art
In satellite based cellular communications systems, a central terrestrial control processor or network operations center (NOC) generally controls one or more communications satellites operating within the communications system. Each communications satellite within the communications system services multiple users located in multiple geographic areas known as ground cells. The communications satellites receive and transmit data signals to and from the multiple users located at the different positions within the separate ground cells in a point-to-point or point-to-multipoint manner. In a frequency division multiple access (FDMA)/time division multiple access (TDMA) communications system, signals on the same frequency, polarization and time slot are generally reused by different users within spatially separated ground cells because of bandwidth constraints, in order to increase the overall capacity of the system.
However, a disadvantage to users sharing frequency, polarization and time slots is that interference is created between the different users in the spatially separated ground cells. This interference may or may not be significant depending on the antenna beam patterns for the particular communications satellite and on the overall system design parameters. User interference may also be caused from multiple users utilizing adjacent frequencies near the boundaries between ground cells when the users are not ideally contained or restricted to their assigned frequency channels. Moreover, users assigned opposite polarizations but overlapping frequencies can also experience mutual interference since the transmit and receive antennas between the user and communications satellite cannot maintain perfect orthogonality between right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) signals. In addition, other orthogonality destroying effects may further be caused by rain induced depolarization of the data signals.
In general, the above-noted interference is magnified in conventional satellite based cellular communications systems. The reason for this is that conventional satellite based cellular communications systems simply assign user frequencies, polarizations and time slots based on a non-adaptive adhoc scheme. These schemes generally are performed on a first come first serve basis using only random selection of user frequencies, polarizations (if applicable) and time slots between the various users. Such conventional satellite based cellular communications systems have much greater levels of intra-system interference and thus, reduced traffic carrying capacity and reduced overall efficiency.
What is needed then is a method for interference management of a processing communications satellite which does not suffer from the above mentioned disadvantages. This will, in turn, provide a satellite based cellular communications system which utilizes intelligent frequency, polarization and time slot assignments; reduces intra-system interference; provides a communications uplink which reduces the required transmit power, terminal complexity and cost; provides a communications downlink which reduces the communications satellite size, weight and power consumption; provides a reduced cost per beam based upon the reduced satellite size, weight and power consumption; provides service to more geographic regions for a given size communications satellite; provides more traffic carrying capacity; provides greater systems revenues; and provides improved service quality to the end users. It is, therefore, an object of the present invention to provide a communications system which utilizes a method for interference management of a processing communications satellite.